Due to the annual motion of the Earth in its orbit, nearby stars move slightly relative to distant "fixed" stars. For a year, such a star describes a small ellipse in the celestial sphere, the size of which is the smaller the further the star is. In angular measure, the semi-major axis of this ellipse is approximately equal to the value of the maximum angle at which 1 AU is visible from the star. e. (semi-major axis of the earth's orbit), perpendicular to the direction of the star. This angle (), called the annual or trigonometric parallax of the star, equal to half of its apparent displacement per year, is used to measure the distance to it based on trigonometric ratios between the sides and angles of the ZSA triangle, in which the angle and basis are known - the semi-major axis of the earth's orbit (cm Fig. 1).

Figure 1. Determination of the distance to the star by the parallax method (A - star, W - Earth, C - Sun).

Distance r to the star, determined by the magnitude of its trigonometric parallax, is equal to:

r = 206265 "" / (a.u.),

where parallax is expressed in arc seconds.

For the convenience of determining distances to stars using parallaxes, a special unit of length is used in astronomy - parsec (ps). A star located at a distance of 1 ps has a parallax of 1 "". According to the above formula, 1 ps = 206265 amu. e. = 3.086 10 18 cm.

Along with the parsec, another special unit of distance is used - a light year (that is, the distance that light travels in 1 year), it is equal to 0.307 ps, or 9.46 10 17 cm.

The closest star to the solar system - a red dwarf of 12th magnitude Proxima Centauri - has a parallax of 0.762, i.e., the distance to it is 1.31 ps (4.3 light years).

The lower limit of measurement of trigonometric parallaxes is ~ 0.01 "", therefore, they can be used to measure distances not exceeding 100 ps with a relative error of 50%. (At distances up to 20 ps, ​​the relative error does not exceed 10%.) This method has been used to determine distances up to about 6000 stars. Distances to more distant stars in astronomy are determined mainly by the photometric method.

Table 1. Twenty nearest stars.

Proxima Centauri.

Here's a classic backfill question. Ask your friends, " Which one is the closest to us?"and then watch how they list nearby stars... Maybe Sirius? Alpha is there something? Betelgeuse? The obvious answer is this; a massive ball of plasma located about 150 million kilometers from Earth. Let's clarify the question. Which star is closest to the Sun?

Nearest star

You've probably heard that it is the third brightest star in the sky at a distance of only 4.37 light years from. But Alpha Centauri not a single star, it is a system of three stars. First, a double star (binary star) with a common center of gravity and an orbital period of 80 years. Alpha Centauri A is only slightly more massive and brighter than the Sun, and Alpha Centauri B is slightly less massive than the Sun. This system also contains a third component, a dull red dwarf Proxima Centauri.

Proxima Centauri- That's what it is the closest star to our sun located at a distance of only 4.24 light years.

Proxima Centauri.

Multiple star system Alpha Centauri located in the constellation Centaurus, which is visible only in the southern hemisphere. Unfortunately, even if you see this system, you will not be able to see Proximu Centauri... This star is so faint that you need a powerful enough telescope to see it.

Let's figure out the scale of how far Proxima Centauri from U.S. Think about. moves at a speed of almost 60,000 km / h, the fastest in. He covered this path in 2015 in 9 years. Traveling fast enough to get to Proxima Centauri, New Horizons will take 78,000 light years.

Proxima Centauri is the closest star over 32,000 light years, and it will hold this record for another 33,000 years. It will make its closest approach to the Sun in about 26,700 years, when the star is only 3.11 light years away from Earth. In 33,000 years, the nearest star will be Ross 248.

What about the northern hemisphere?

For those of us in the northern hemisphere, the closest visible star is Barnard's Star, another red dwarf in the constellation Ophiuchus. Unfortunately, like Proxima Centauri, Barnard's Star is too dim to see with the naked eye.

Barnard's Star.

Nearest star that you can see with the naked eye in the northern hemisphere is Sirius (Alpha Canis Major)... Sirius is twice the size and mass of the Sun and is the brightest star in the sky. Located 8.6 light years away in the constellation Canis Major, it is the most famous star that stalks Orion in the night sky in winter.

How did astronomers measure the distance to the stars?

They use a method called. Let's do a little experiment. Keep one arm outstretched and place your finger so that there is some distant object nearby. Now open and close each eye in turn. Notice how your finger seems to jump back and forth when you look with different eyes. This is the parallax method.

Parallax.

To measure the distance to the stars, you can measure the angle to the star in relation to when the Earth is on one side of the orbit, say in the summer, then 6 months later, when the Earth moves to the opposite side of the orbit, and then measure the angle to the star relative to what - any distant object. If the star is close to us, this angle can be measured and the distance calculated.

You can actually measure the distance in this way up to nearby stars but this method only works up to 100 "000 light years.

20 closest stars

Here is a list of the 20 closest star systems and their distance in light years. Some of them have multiple stars, but they are part of the same system.

According to NASA, there are 45 stars within a 17 light-year radius of the Sun. There are over 200 billion stars in the world. Some are so dim that they are nearly impossible to detect. Perhaps with new technologies, scientists will find stars even closer to us.

Title of the article you read "The closest star to the Sun".

How to determine the distance to the stars? How is it known that Alpha Centauri is about 4 light years away? Indeed, by the brightness of a star, as such, little can be determined - the brightness of a dim close and bright distant stars can be the same. And yet there are many fairly reliable ways to determine the distance from the Earth to the farthest corners of the universe. Astrometric satellite "Hipparchus" for 4 years of work determined the distance to 118 thousand stars SPL

No matter what physicists say about three-dimensionality, six-dimensionality or even eleven-dimensionality of space, for an astronomer the observable Universe is always two-dimensional. What is happening in Space is seen by us in the projection onto the celestial sphere, just as in the cinema the entire complexity of life is projected onto a flat screen. On the screen, we can easily distinguish far from close thanks to our acquaintance with the volumetric original, but in the two-dimensional scattering of stars there is no visual clue that allows us to turn it into a three-dimensional map suitable for plotting the course of an interstellar ship. Meanwhile, distances are the key to almost half of all astrophysics. How to distinguish a nearby dim star from a distant but bright quasar without them? Only knowing the distance to the object, you can estimate its energy, and hence the direct road to understanding its physical nature.

A recent example of the uncertainty of cosmic distances is the problem of sources of gamma-ray bursts, short pulses of hard radiation, coming to Earth from different directions about once a day. Initial estimates of their distance ranged from hundreds of astronomical units (tens of light hours) to hundreds of millions of light years. Accordingly, the scatter in the models was also impressive - from annihilation of comets from antimatter on the outskirts of the Solar System to explosions of neutron stars shaking the entire Universe and the birth of white holes. By the mid-1990s, more than a hundred different explanations for the nature of gamma-ray bursts had been proposed. Now that we have been able to estimate the distances to their sources, there are only two models left.

But how to measure the distance if you cannot reach the object with either a ruler or a locator beam? The triangulation method, widely used in conventional earth geodesy, comes to the rescue. We select a segment of a known length - a base, measure from its ends the angles at which a point inaccessible for one reason or another is visible, and then simple trigonometric formulas give the desired distance. When we move from one end of the base to the other, the apparent direction to the point changes, it shifts against the background of distant objects. This is called parallax offset, or parallax. Its value is smaller, the further the object is, and the larger, the longer the base.

To measure distances to stars, one has to take the maximum base available to astronomers, equal to the diameter of the earth's orbit. The corresponding parallax displacement of stars in the sky (strictly speaking, half of it) began to be called the annual parallax. Tycho Brahe tried to measure it, who did not like Copernicus's idea of ​​the Earth's rotation around the Sun, and he decided to test it - parallaxes also prove the Earth's orbital motion. The measurements carried out had an impressive accuracy for the 16th century - about one minute of an arc, but this was completely insufficient to measure the parallaxes, which Brahe himself did not suspect and concluded that the Copernican system was incorrect.

Distance to star clusters is determined by main sequence fitting

The next attack on parallax was undertaken in 1726 by the Englishman James Bradley, the future director of the Greenwich Observatory. At first, it seemed that he was lucky: the star selected for observations, the Dragon gamma, actually fluctuated around its average position with a span of 20 arc seconds for a year. However, the direction of this displacement was different from what was expected for parallaxes, and Bradley soon found the correct explanation: the speed of the Earth's orbit adds up with the speed of light coming from the star, and changes its apparent direction. Likewise, raindrops leave inclined paths on the windows of the bus. This phenomenon, called the annual aberration, was the first direct evidence of the Earth's motion around the Sun, but had nothing to do with parallaxes.

Only a century later, the accuracy of goniometric instruments has reached the required level. In the late 1830s, as John Herschel put it, "the wall that prevented penetration into the stellar Universe was breached almost simultaneously in three places." In 1837, Vasily Yakovlevich Struve (at that time the director of the Dorpat observatory, and later the Pulkovo observatory) published the Vega parallax measured by him - 0.12 arc seconds. The next year, Friedrich Wilhelm Bessel reported that the parallax of the 61st Cygnus star is 0.3 ". And a year later, the Scottish astronomer Thomas Henderson, who worked in the Southern Hemisphere at the Cape of Good Hope, measured the parallax in the alpha Centauri system - 1.16" ... True, it later turned out that this value was overestimated by a factor of 1.5, and in the entire sky there is not a single star with a parallax of more than 1 arc second.

For distances measured by the parallax method, a special unit of length was introduced - parsec (from parallax second, pc). One parsec contains 206,265 astronomical units, or 3.26 light years. It is from this distance that the radius of the earth's orbit (1 astronomical unit = 149.5 million kilometers) is visible at an angle of 1 second. To determine the distance to a star in parsecs, you need to divide one by its parallax in seconds. For example, to the closest star system, Alpha Centauri, 1 / 0.76 = 1.3 parsecs, or 270 thousand astronomical units. A thousand parsecs is called a kiloparsec (kpc), a million parsecs is a megaparsec (Mpc), and a billion is a gigaparsec (Gpc).

Measuring extremely small angles required technical sophistication and great diligence (Bessel, for example, processed more than 400 individual observations of the 61st Cygnus), but after the first breakthrough things went easier. By 1890, the parallaxes of three dozen stars had already been measured, and when photography began to be widely used in astronomy, the exact measurement of parallaxes was completely put on stream. Parallax measurement is the only method for directly determining the distances to individual stars. However, during ground-based observations, atmospheric noise does not allow the parallax method to measure distances over 100 pc. For the Universe, this is not a very large value. (“It's not far here, there are a hundred parsecs,” as Gromozeka used to say.) Where geometric methods fail, photometric methods come to the rescue.

Geometric records

In recent years, the results of measuring the distances to very compact sources of radio emission - masers - have been published more and more often. Their radiation falls within the radio range, which makes it possible to observe them on radio interferometers capable of measuring the coordinates of objects with a microsecond precision, unattainable in the optical range in which stars are observed. Thanks to masers, trigonometric methods can be applied not only to distant objects in our Galaxy, but also to other galaxies. For example, in 2005 Andreas Brunthaler (Germany) and his colleagues determined the distance to the M33 galaxy (730 kpc) by comparing the angular displacement of the masers with the rotation speed of this stellar system. A year later, Ye Xu (China) and his colleagues applied the classical parallax method to "local" maser sources to measure the distance (2 kpc) to one of the spiral arms of our Galaxy. Perhaps the most advanced in 1999 was J. Hernsteen (USA) and his colleagues. Tracking the motion of masers in the accretion disk around the black hole in the core of the active galaxy NGC 4258, astronomers have determined that this system is at a distance of 7.2 Mpc from us. Today it is an absolute record for geometric methods.

Astronomers' Standard Candles

The further away from us the radiation source is, the dimmer it is. If you know the true luminosity of an object, then by comparing it with the apparent brightness, you can find the distance. Huygens was probably the first to apply this idea to measuring distances to stars. At night he watched Sirius, and during the day he compared its brilliance with a tiny hole in the screen that covered the Sun. Having chosen the size of the hole so that both brightness coincided, and comparing the angular values ​​of the hole and the solar disk, Huygens concluded that Sirius is 27,664 times farther from us than the Sun. This is 20 times less than the real distance. Part of the error was due to the fact that Sirius is actually much brighter than the Sun, and partly due to the difficulty of comparing brightness from memory.

A breakthrough in the field of photometric methods happened with the advent of photography into astronomy. At the beginning of the 20th century, the Harvard College Observatory carried out a large-scale work to determine the brightness of stars from photographic plates. Particular attention was paid to variable stars, whose brightness fluctuates. Studying variable stars of a special class - Cepheids - in the Small Magellanic Cloud, Henrietta Levitt noticed that the brighter they are, the longer the period of their brightness fluctuations: stars with a period of several tens of days turned out to be about 40 times brighter than stars with a period of the order of a day.

Since all Levitt Cepheids were in the same star system - the Small Magellanic Cloud - it could be assumed that they were removed from us at the same (albeit unknown) distance. This means that the difference in their apparent brightness is associated with real differences in luminosity. It remained to determine the geometrical method of the distance to one Cepheid in order to calibrate the entire dependence and to get the opportunity, by measuring the period, to determine the true luminosity of any Cepheid, and from it the distance to the star and the star system containing it.

But, unfortunately, there are no Cepheids in the vicinity of the Earth. The closest of them - the North Star - is distant from the Sun, as we now know, by 130 pc, that is, it is out of reach for ground-based parallax measurements. This did not allow throwing the bridge directly from the parallaxes to the Cepheids, and astronomers had to erect a structure that is now figuratively called the staircase of distances.

Open star clusters, including from several tens to hundreds of stars, connected by a common time and place of birth, became an intermediate step on it. If you plot the temperature and luminosity of all the stars in the cluster, most of the points fall on one oblique line (more precisely, a strip), which is called the main sequence. Temperature is determined with high accuracy by the spectrum of a star, and luminosity is determined by apparent brightness and distance. If the distance is unknown, the fact that all the stars in the cluster are almost equally distant from us again comes to the rescue, so that within the cluster, the apparent brightness can still be used as a measure of luminosity.

Since the stars are the same everywhere, the main sequences for all clusters must be the same. The differences are only due to the fact that they are at different distances. If we determine the distance to one of the clusters by a geometric method, then we will find out what the “real” main sequence looks like, and then, by comparing the data on other clusters with it, we will determine the distances to them. This technique is called "main sequence fitting". For a long time, the Pleiades and Hyades served as a standard for him, the distances to which were determined by the method of group parallaxes.

Fortunately for astrophysics, Cepheids have been found in about two dozen open clusters. Therefore, by measuring the distances to these clusters by fitting the main sequence, it is possible to "reach the ladder" to the Cepheids, which find themselves on its third stage.

As an indicator of distances, Cepheids are very convenient: there are relatively many of them - they can be found in any galaxy and even in any globular cluster, and being giant stars, they are bright enough to measure intergalactic distances from them. Thanks to this, they have earned many high-profile epithets, such as "beacons of the Universe" or "milestones of astrophysics." The Cepheid "ruler" stretches up to 20 Mpc, which is about a hundred times the size of our Galaxy. Then they can no longer be distinguished even in the most powerful modern instruments, and in order to climb the fourth rung of the ladder of distances, you need something brighter.

To the outskirts of the universe

One of the most powerful extragalactic distance measurements is based on a pattern known as the Tully-Fisher relationship: the brighter a spiral galaxy, the faster it spins. When a galaxy is viewed edge-on or at a significant tilt, half of its material is approaching us due to rotation, and half is receding, which leads to broadening of spectral lines due to the Doppler effect. This expansion is used to determine the speed of rotation, from it - the luminosity, and then from comparison with the apparent brightness - the distance to the galaxy. And, of course, to calibrate this method, galaxies are needed, the distances to which have already been measured by Cepheids. The Tully - Fisher method is very long-range and covers galaxies hundreds of megaparsecs distant from us, but it also has a limit, since for galaxies that are too distant and faint, it is not possible to obtain sufficiently high-quality spectra.

In a slightly larger range of distances, another "standard candle" is active - type Ia supernovae. The outbursts of such supernovae are "the same type" thermonuclear explosions of white dwarfs with a mass slightly above the critical mass (1.4 solar masses). Therefore, there is no reason for them to vary greatly in power. Observations of such supernovae in nearby galaxies, the distances to which can be determined from the Cepheids, seem to confirm this constancy, and therefore cosmic thermonuclear explosions are now widely used to determine distances. They are visible even in billions of parsecs from us, but you never know the distance to which galaxy you will be able to measure, because it is not known in advance exactly where the next supernova will break out.

So far, only one method allows you to go even further - redshifts. Its history, like the history of the Cepheids, begins simultaneously with the 20th century. In 1915, the American Vesto Slipher, studying the spectra of galaxies, noticed that in most of them the lines are shifted towards the red side relative to the "laboratory" position. In 1924, the German Karl Wirtz noticed that the smaller the angular dimensions of the galaxy, the stronger this displacement. However, only Edwin Hubble in 1929 managed to bring these data into a single picture. According to the Doppler effect, the redshift of lines in the spectrum means that the object is moving away from us. Comparing the spectra of galaxies with the distances to them, determined by the Cepheids, Hubble formulated the law: the speed of a galaxy's receding is proportional to the distance to it. The proportionality coefficient in this ratio is called the Hubble constant.

Thus, the expansion of the Universe was discovered, and with it the possibility of determining the distances to galaxies from their spectra, of course, provided that the Hubble constant is tied to some other "rulers". Hubble himself performed this binding with an error of almost an order of magnitude, which was corrected only in the mid-1940s, when it became clear that Cepheids are divided into several types with different period-luminosity ratios. The calibration was performed anew based on the "classical" Cepheids, and only then the value of the Hubble constant became close to modern estimates: 50-100 km / s for each megaparsec of distance to the galaxy.

Now, redshifts are used to determine distances to galaxies that are thousands of megaparsecs away from us. True, in megaparsecs, these distances are indicated only in popular articles. The fact is that they depend on the model of the evolution of the Universe adopted in the calculations, and, moreover, in the expanding space it is not entirely clear what distance is meant: the one at which the galaxy was at the moment of emission of radiation, or the one at which it is located at the moment of its reception on Earth, or the distance traveled by light on the way from the starting point to the final one. Therefore, astronomers prefer to indicate for distant objects only the directly observed value of the redshift, without converting it into megaparsecs.

Red shifts are currently the only method for estimating "cosmological" distances comparable to the "size of the Universe", and at the same time it is, perhaps, the most widespread technique. In July 2007, a catalog of redshifts of 77 418 767 galaxies was published. True, during its creation, a somewhat simplified automatic technique for analyzing spectra was used, and therefore errors could creep into some values.

Team play

Geometric methods for measuring distances are not limited to annual parallax, in which the apparent angular displacements of stars are compared with the displacements of the Earth in orbit. Another approach relies on the movement of the sun and stars relative to each other. Imagine a star cluster flying past the Sun. According to the laws of perspective, the visible trajectories of its stars, like rails on the horizon, converge at one point - the radiant. Its position indicates at what angle the cluster flies to the line of sight. Knowing this angle, one can decompose the motion of the cluster stars into two components - along the line of sight and perpendicular to it along the celestial sphere - and determine the proportion between them. The radial velocity of stars in kilometers per second is measured by the Doppler effect and, taking into account the found proportion, the projection of the velocity onto the sky is calculated - also in kilometers per second. It remains to compare these linear velocities of the stars with the angular ones determined from the results of long-term observations - and the distance will be known! This method works up to several hundred parsecs, but is applicable only to star clusters and is therefore called the group parallax method. This is how the distances to the Hyades and the Pleiades were first measured.

Down the stairs leading up

Building our staircase to the outskirts of the Universe, we were silent about the foundation on which it rests. Meanwhile, the parallax method gives the distance not in standard meters, but in astronomical units, that is, in the radii of the earth's orbit, the value of which was also not immediately determined. So let's look back and go down the stairs of cosmic distances to Earth.

Probably, the first to try to determine the remoteness of the Sun was Aristarchus of Samos, who proposed a heliocentric system of the world one and a half thousand years before Copernicus. He turned out that the Sun is 20 times farther from us than the Moon. This estimate, as we now know, underestimated by a factor of 20, held out until the Kepler era. Although he himself did not measure the astronomical unit, he already noted that the Sun should be much further than Aristarchus believed (and all other astronomers behind him).

Over the next two centuries, the transit of Venus along the solar disk became the main tool for determining the scale of the solar system. Observing them simultaneously from different points of the globe, you can calculate the distance from Earth to Venus, and hence all other distances in the solar system. In the 18th-19th centuries, this phenomenon was observed four times: in 1761, 1769, 1874 and 1882. These observations were among the first international scientific projects. Large-scale expeditions were outfitted (the English expedition of 1769 was led by the famous James Cook), special observation stations were created ... And if at the end of the 18th century Russia only provided French scientists with the opportunity to observe the passage from its territory (from Tobolsk), scientists have already taken an active part in research. Unfortunately, the extreme complexity of the observations has led to a significant discrepancy in the estimates of the astronomical unit - from about 147 to 153 million kilometers. A more reliable value - 149.5 million kilometers - was obtained only at the turn of the XIX-XX centuries from the observations of asteroids. And, finally, it should be borne in mind that the results of all these measurements were based on knowledge of the length of the base, in the role of which, when measuring the astronomical unit, was the radius of the Earth. So ultimately the foundation of the space-distance ladder was laid by surveyors.

Only in the second half of the 20th century at the disposal of scientists appeared fundamentally new methods of determining space distances - laser and radar. They made it possible to increase the accuracy of measurements in the solar system by hundreds of thousands of times. The radar error for Mars and Venus is several meters, and the distance to the corner reflectors installed on the Moon is measured with an accuracy of centimeters. The currently accepted value of the astronomical unit is 149,597,870,691 meters.

The difficult fate of "Hipparchus"

Such a radical progress in measuring the astronomical unit has raised the question of distances to stars in a new way. The accuracy of determining parallaxes is limited by the Earth's atmosphere. Therefore, back in the 1960s, the idea arose to launch a goniometric instrument into space. It was realized in 1989 with the launch of the European astrometric satellite "Hipparchus". This name is a well-established, although formally and not entirely correct, translation of the English name HIPPARCOS, which is an abbreviation for High Precision Parallax Collecting Satellite ("satellite for collecting high-precision parallaxes") and does not coincide with the English spelling of the name of the famous ancient Greek astronomer - Hipparchus, the author of the first star catalog.

The expedition began with trouble. Due to a failure in the upper stage, Hipparchus did not enter the calculated geostationary orbit and remained on an intermediate, highly elongated trajectory. The specialists of the European Space Agency managed to cope with the situation, and the orbiting astrometric telescope successfully worked for 4 years. The processing of the results took the same amount of time, and in 1997 a stellar catalog with parallaxes and proper motions of 118,218 luminaries, including about two hundred Cepheids, was published.

Unfortunately, on a number of issues, the desired clarity did not come. The most incomprehensible result was for the Pleiades - it was assumed that "Hipparchus" would clarify the distance, which was previously estimated at 130-135 parsecs, but in practice it turned out that "Hipparchus" corrected it, having received a value of only 118 parsecs. Acceptance of a new value would require an adjustment of both the theory of stellar evolution and the scale of intergalactic distances. This would become a serious problem for astrophysics, and the distance to the Pleiades began to be carefully checked. By 2004, several groups independently obtained estimates of the distance to the cluster in the range from 132 to 139 pc. Offensive voices began to be heard, suggesting that the consequences of putting the satellite into the wrong orbit still could not be completely eliminated. Thus, in general, all parallaxes measured by him were called into question.

The Hipparchus team was forced to admit that the measurements are generally accurate, but may need to be re-processed. The point is that parallaxes are not directly measured in space astrometry. Instead, Hipparchus measured the angles between numerous pairs of stars over the course of four years. These angles change both due to the parallax displacement and due to the proper motions of the stars in space. To "extract" the parallax values ​​from the observations, a rather complex mathematical processing is required. It was this that had to be repeated. The new results were published at the end of September 2007, but it is not yet clear how much this has improved.

Aristotle's universe ended at nine distances from the Earth to the Sun. Copernicus believed that the stars are 1,000 times farther than the Sun. Parallaxes pushed even nearby stars light years away. At the very beginning of the 20th century, the American astronomer Harlow Shapley, using Cepheids, determined that the diameter of the Galaxy (which he identified with the Universe) is measured in tens of thousands of light years, and thanks to Hubble, the boundaries of the Universe expanded to several gigaparsecs. How final are they?

Of course, at each rung of the ladder of distances, its own, larger or smaller errors arise, but on the whole, the scales of the Universe are determined quite well, tested by different methods independent of each other and add up to a single consistent picture. So the modern boundaries of the universe seem to be immutable. However, this does not mean that one fine day we will not want to measure the distance from it to some neighboring Universe!

On February 22, 2017, NASA reported that 7 exoplanets were found near the single TRAPPIST-1 star. Three of them are in the range of distances from the star in which the planet can have liquid water, and water is a key condition for life. It is also reported that this star system is located at a distance of 40 light-years from Earth.

This message caused a lot of noise in the media, it even seemed to some that humanity is on the verge of building new settlements near a new star, but this is not so. But 40 light years is a lot, it is a LOT, it is too many kilometers, that is, this is a monstrously colossal distance!

From the physics course, the third cosmic speed is known - this is the speed that a body must have at the surface of the Earth in order to go beyond the solar system. The value of this speed is 16.65 km / s. Orbital spacecraft take off at a speed of 7.9 km / sec and revolve around the Earth. In principle, a speed of 16-20 km / sec is quite accessible to modern earth technologies, but no more!

Humanity has not yet learned how to accelerate spaceships faster than 20 km / sec.

Let's calculate how many years it will take for a spaceship traveling at a speed of 20 km / s to travel 40 light years and reach the star TRAPPIST-1.
One light year is the distance that a ray of light travels in a vacuum, and the speed of light is approximately 300 thousand km / sec.

A spacecraft made by human hands travels at a speed of 20 km / sec, that is, 15,000 times slower than the speed of light. Such a ship will cover 40 light years in a time equal to 40 * 15000 = 600000 years!

An earth ship (with the current level of technology) will reach the TRAPPIST-1 star in about 600 thousand years! Homo sapiens has existed on Earth (according to scientists) only 35-40 thousand years, and here it is as much as 600 thousand years!

In the near future, technology will not allow humans to reach the TRAPPIST-1 star. Even promising engines (ionic, photonic, space sails, etc.), which do not exist in earthly reality, are estimated to be able to accelerate the ship to a speed of 10,000 km / s, which means that the flight time to the TRAPPIST-1 system will be reduced to 120 years. ... This is already a more or less acceptable time for flying with the help of suspended animation or for several generations of settlers, but today all these engines are fantastic.

Even the nearest stars are still too far from people, too far, not to mention the stars of our Galaxy or other galaxies.

The diameter of our Milky Way galaxy is about 100 thousand light years, that is, the path from end to end for a modern Earth ship will be 1.5 billion years! Science suggests that our Earth is 4.5 billion years old, and multicellular life is about 2 billion years old. The distance to the nearest galaxy to us - the Andromeda Nebula - is 2.5 million light years from Earth - what a monstrous distance!

As you can see, of all living people, no one will ever set foot on the earth of a planet near another star.

How can you measure the distance to the stars?

Horizontal parallax method

The globe, keeping at a distance of 149.6 million kilometers from the Sun, “winds” a very small distance in its orbit during the year.

However, the truly gigantic distances start outside. Only at the beginning of the 20th century, scientists were able to make sufficiently accurate measurements and for the first time establish the distance to some stars.

The way to determine the distance to the stars is to accurately determine the direction to them (that is, to determine their position on) from both ends of the diameter of the earth's orbit and is called "Horizontal parallax method"... To do this, it is only necessary to determine the direction to the star at moments separated from each other by six months, since the Earth during this time itself carries the observer with itself from one side of its orbit to the other.

The displacement of the star (of course, apparent), caused by a change in the position of the observer in space, is extremely small, barely perceptible. But, it was measured with an accuracy of 0 ″, 01. Is it a lot or a little? Judge for yourself - it's like looking at the edge of a coin thrown by passers-by in Moscow on Red Square from Ryazan.

It is clear that with such distances and distances, the meters and kilometers we are used to are no longer good for anything. Really large, that is, cosmic distances, it is more convenient to express not in kilometers, but in light years, that is, in those distances that light, propagating at a speed of 300,000 km / s, runs over a year.

Using the described method, you can determine the distance to stars that are much further away than three hundred light years. Starlight from some distant stellar systems reaches us hundreds of millions of light years away.

This does not mean at all, as is often thought, that we are observing stars that may no longer exist in reality now. It is not necessary to say that "we see in the sky that which in reality is no longer there." Indeed, the vast majority of stars change so slowly that millions of years ago they were the same as they are now, and even their visible places in the sky change extremely slowly, although stars move rapidly in space. Thus, the stars as we see them are, in general, the same at the present time.